Typically, a computer system includes a number of integrated circuit chips that communicate with one another to perform system applications. As chip speeds increase, the amount of data communicated between chips increases to meet the demands of some system applications. Often, the computer system includes a controller, such as a micro-processor, and one or more memory chips, such as random access memory (RAM) chips. The RAM chips can be any suitable type of RAM, such as dynamic RAM (DRAM), double data rate synchronous DRAM (DDR-SDRAM), graphics DDR-SDRAM (GDDR-SDRAM), reduced latency DRAM (RLDRAM), pseudo static RAM (PSRAM), and low power DDR-SDRAM (LPDDR-SDRAM).
Many of the integrated circuit chips, such as the memory chips, receive a clock signal to operate. In a memory chip operating at high frequencies, it is important to have a clock signal that has about a 50% duty cycle. This provides the memory with approximately an equal amount of time on the high level phase and the low level phase of a clock cycle for transferring data, such as latching rising edge data and latching falling edge data, into and out of the memory.
Typically, a clock signal is provided by an oscillator, such as a crystal oscillator, and clock circuitry. The oscillator and clock circuitry often provide a clock signal that does not have a 50% duty cycle. For example, the clock signal may have a 45% duty cycle, where the high level phase is 45% of one clock cycle and the low level phase is the remaining 55% of the clock cycle. To correct or change the duty cycle of the clock signal, a duty cycle detector can indicate the duty cycle of the clock signal and the output of the duty cycle detector can be provided to the clock circuitry that corrects the clock signal to have about a 50% duty cycle.
Duty cycle detectors are usually either analog duty cycle detectors or digital duty cycle detectors. Analog duty cycle detectors often require big design efforts and even in power saving mode an analog duty cycle detector consumes power. Digital duty cycle detectors often include fine delay units that are difficult to build and complex control circuitry.
For these and other reasons there is a need for the present invention.